A large number of patents have reported the preparation of monoazo dyestuffs from heterocyclic amine bases which are diazotized and reacted with an N-substituted aniline coupler. Some patents describe couplers containing N-hydroxyalkyl substitution, such as Dickey, U.S. Pat. No. 2,683,708. Although some of te compounds have been satisfactory for the dyeing of various cellulose acetate fibers, it has been found that the fastness properties of such dyestuffs are inadequate for use on polyester.
In accordance with the invention, I have discovered a new dyestuff mixture providing excellent blue dyeings on polyester fibers, particularly polyethylene terephthalate.